The present application is based on and claims priority from Japanese Patent Application Hei 11-332251 filed Nov. 24, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnet switch having a resinous switch cover and a metal member that is insert-molded into the switch cover.
2. Description of the Related Art
JP-A-11-213087 discloses a conventional magnet switch. The magnet switch includes a resinous case, a cylindrical metal member fixed to the resinous case, an external terminal comprised of a bolt inserted into the inside of the metal member, and a nut screwed to external terminal. The metal member is designed to receive the fastening force of nut.
When a creep appears due to natural aging process in the resinous case of such a magnet switch as includes the metal member insert-molded into the resinous case, cracks form around the metal member, and the sealing performance of the resinous case deteriorates. Particularly, such cracks may form in the magnet switch of a starter under a high temperature caused by a large amount of electric current flowing through the magnet switch. Therefore, the sealing performance of the portion around the external terminal is very important.
In the above-described magnet switch, two O-rings are respectively inserted into gaps between the metal member and the external terminal and between the metal member and the resinous case so that the gaps inside and outside of metal member can be sealed. However, the above sealing structure necessarily increases the number of parts and becomes complicated. This also increases the cost of the magnet switch.
The invention has been made in view of the above circumstances. The object of the invention is to provide an inexpensive magnet switch having a simple sealing structure around the external terminal.
Features of the present invention are as follows:
a head of the external terminal has a first sealing surface; a switch cover has a second sealing surface opposite the first sealing surface; and a seal member is disposed in a gap between the first and second sealing surfaces to seal the gap.
According to the above feature, only a single sealing member is necessary, so that the sealing structure can be made simple, and the number of parts can be reduced. Therefore, such a magnet switch can be manufactured at a low cost.
Preferably, the head of the external terminal has a first perpendicular surface that is approximately perpendicular to the axial direction of the terminal at a side facing the screw portion. The switch cover has a second annular perpendicular surface facing the first perpendicular surface of the head; and a seal member is disposed in the gap between the first and second perpendicular surfaces to seal the gap.
In the above magnet switch, it is preferable to provide the following features: the head of the external terminal includes a rotation stopper portion having a polygonal outer periphery and a cylindrical portion having a cylindrical outer periphery; and the cylindrical portion is formed stepwise at a side of the rotation stopper portion facing the screw portion.
In the above magnet switch, it is more preferable to provide the following feature: the outer periphery of the metal member insert-molded into the switch cover has a corrugated surface in the longitudinal direction. It is possible to provide a long boundary between the metal member and the switch cover to improve the sealing performance. The corrugated surface can fix the metal member to the switch cover effectively.